Synthesis of biliverdin and bilirubin 1-O-acyl-beta-D-glucopyranuronic acids

Chemical synthesis of 24-β-d-galactopyranosides of bile acids: a new type of bile acid conjugates in human urine

A method is reported for the preparation of the C-24 carboxyl-linked beta-D-galactopyranosides of lithocholic, deoxycholic, chenodeoxycholic, ursodeoxycholic, and cholic acids, two of which were recently identified as a novel type of the metabolites of bile acids excreted in human urine. Direct esterification (galactosidation) of the unprotected bile acids with 2,3,4,6-tetra-O-benzyl-D-galactopyranose in the presence of 2-chloro-1,3,5-trinitrobenzene as a coupling agent and subsequent hydrogenolysis of the resulting benzyloxy-protected bile acid 24-beta-D-galactopyranosides over 10% palladium on charcoal under atmospheric pressure afforded the title compounds. The structures of the bile acid acyl galactosides were confirmed by measuring several (1)H-(1)H and (1)H-(13)C shift correlated 2D NMR.

Capillary gas chromatographic separation of bile acid acyl glycosides without thermal decomposition and isomerization

A direct method for the capillary gas chromatographic (cGC) separation of the acyl glycosides of bile acids was successfully attained. The free acyl glycosides were derivatized to their complete trifluoroacetyl (TFA) derivatives with N-methyl-bis(trifluoroacetamide). The highly volatile TFA derivatives were chromatographed on a short-length (10 m), narrow-bore (0.1 mm) capillary column coated with a thin film (0.1 microm) of 5% phenyl polysilphenylene-siloxane at a column temperature below 280 degrees C. Each exhibited a single, well-separated peak of the theoretical shape without any accompanying peaks due to the thermal decomposition and isomerization. The bile acid 24alpha-glucosides were always eluted faster than the corresponding 24beta-glucosides, which eluted before the corresponding 24beta-galactosides. The method could be usefully applied to biosynthetic and metabolic studies of bile acid acyl glycosides in biological materials.

Potential bile acid metabolites. 24. An efficient synthesis of carboxyl-linked glucosides and their chemical properties

A facile and efficient synthesis of the carboxyl-linked glucosides of bile acids is described. Direct esterification of unprotected bile acids with 2,3,4,6-tetra-O-benzyl-D-glucopyranose in pyridine in the presence of 2-chloro-1,3,5-trinitrobenzene as a coupling agent afforded a mixture of the alpha- and beta-anomers (ca. 1:3) of the 1-O-acyl-D-glucoside benzyl ethers of bile acids, which was separated effectively on a C18 reversed-phase chromatography column (isolated yields of alpha- and beta-anomers are 4-9% and 12-19%, respectively). Subsequent hydrogenolysis of the alpha- and beta-acyl glucoside benzyl ethers on a 10% Pd-C catalyst in acetic acid/methanol/EtOAc (1:2:2, by vol) at 35 degrees C under atmospheric pressure gave the corresponding free esters in good yields (79-89%). Chemical specificities such as facile hydrolysis and transesterification of the acyl glucosides in various solvents were also discussed.

Separatory determination of diastereomeric ibuprofen glucuronides in human urine by liquid chromatography/electrospray ionization-mass spectrometry

A method for the separatory determination of diastereomeric isomers of glucuronic acid conjugates of ibuprofen having a carboxyl group at the chiral center by liquid chromatography (LC)/electrospray ionization (ESI)-mass spectrometry (MS) has been developed. The authentic specimens of acyl glucuronides of R(-)- and S(+)-ibuprofen were chemically synthesized by the Mitsunobu reaction. In the ESI mode, the glucuronides were characterized by an abundant quasi-molecular ion [M-H]-, and the formation of the negative ion was markedly influenced by a drift voltage. The resolution of diastereomeric isomers was achieved on a Develosil ODS-HG-5 column with 20 mM ammonium acetate (pH 5.0):acetonitrile (5:2, v/v) as a mobile phase where diastereomers were monitored with a corresponding quasi-molecular ion. After oral administration of racemic ibuprofen, a preferential excretion of (S)-ibuprofen glucuronide into the urine was observed.

Synthesis of bile acid 24-acyl glucuronides

The synthesis of acyl glucuronides of common bile acids is described. By means of the Mitsunobu reaction employing diethylazodicarboxylate and triphenylphosphine, bile acids were condensed through the inherent C-24 carboxy group with benzyl 2,3,4-tri-O-benzyl-D-glucopyranuronate, which was prepared from 1-O-methyl-alpha-D-glucose. The separation and purification of the beta-anomers at the anomeric position of the sugar moiety were attained by preparative thin-layer chromatography and/or high-performance liquid chromatography on a column packed with phenyl-bonded silica using H2O-MeOH as a mobile phase. The removal of the benzyl group on the sugar moiety was achieved by catalytic hydrogenation with 10% palladium on carbon to yield the desired acyl glucuronides of bile acids. The structures of these acyl glucuronides were confirmed by proton nuclear magnetic resonance spectral properties.

Biosynthesis and chemical synthesis of carboxyl-linked glucuronide of lithocholic acid

The glucuronidation of lithocholic acid (LA) by phenobarbital-induced male Fischer 344 rat liver microsomes supplemented with UDP-glucuronic acid was studied. A single radioactive metabolite was formed and its structure was determined by high pressure liquid chromatography/particle beam/mass spectrometry (HPLC/PB/MS), both with and without prior methylation and acetylation of the sample. The reaction product was rigorously identified as the 1-O-acyl-beta-D-glucuronide of LA by comparison with a chemically synthesized standard. The chemical synthesis of the acyl glucuronide of LA was accomplished via a condensation reaction using benzyl 2,3,4-tri-O-benzyl-D-glucopyranuronate. The latter compound was prepared in two steps from benzyl 2,3,4-tri-O-benzyl-1-O-methyl-alpha-D-glucopyranuronate via the 1-O-acetyl derivative. The stereoselective beta coupling of LA with 2,3,4-tri-O-benzyl-D-glucopyranuronate was achieved by the Mitsunobu reaction, in the presence of the free hydroxyl function of LA, using triphenylphosphine and diisopropyl azodicarboxylate in THF followed by preparative TLC. The benzylic ester and ether groups were cleaved by hydrogenation with Pd on charcoal as the catalyst. Positive identification of the glucuronide was established by HPLC/PB/MS and 1H-NMR spectra. No side products formed by acyl migration were detected, but the free acyl glucuronide underwent rapid transesterification in methanol.

A review of the methods of chemical synthesis of sulphate and glucuronide conjugates

1. Methods for the synthesis of drug conjugates with sulphuric acid have been reviewed. 2. Some analytical methods are presented for the analysis of sulphate conjugates. 3. The synthesis of several types of N, O and C beta-D-glucuronides is reviewed. Different beta-coupling reactions of protected glucuronides are presented. 4. Application of n.m.r. and mass spectrometry to the analysis of beta-D-glucuronides is discussed.

Properties and determination of serum and bilirubin

The accurate determination of the types and amounts of bilirubin species in serum is important for diagnostic purposes as well as for therapeutic monitoring. However, of the determinations routinely performed in the clinical laboratory, those for bilirubins are not among the more accurate and exhibit significant method variability. In this review, the structural, stability, solubility, and albumin-binding properties of serum bilirubins are discussed with respect to their impact on analytical methods. Following a consideration of analytical standards, methods for the determination of unconjugated and conjugated bilirubins are reviewed and recent developments are evaluated. Finally, the present capabilities and future potential of the methods for producing information applicable to the development of new or improved methods of determination are summarized.